Rating System

LEED BD+C: New Construction, LEED BD+C: Core and Shell, LEED BD+C: Schools, LEED ID+C: Commercial Interiors, LEED O+M: Existing Buildings

Rating System Version

v3 - LEED 2008, v2 - Schools 2007, v2 - LEED 2.2, v2 - LEED 2.0

Inquiry

Our question regards the filtration requirement for re-circulating air systems, such as VAV terminals and fan coil units, under EQc5. Per LI 5061 and LI 1795 rulings, "Since the fan coil units re-circulate room air, they must have MERV 13 filters", so do the VAV terminal units that re-circulate air. This conflicts with our previous understanding that the MERV13 requirement would only apply to the air handling units supplying 100% outside air - or a mix of outside and return air - to a single or several rooms. The use of MERV 13 filters is justified when HVAC systems re-circulate a part of return air - e.g. mixed return air streams from various rooms - back to different spaces. In this configuration, supply ducts of the HVAC system and return air may become contaminated by re-circulated indoor-generated pollutants. Thus, contamination generated at specific indoor locations may be spread throughout the building unless properly filtered. However, the use of MERV 13 filters cannot be justified where air is re-circulated within the room. In this configuration, there is no possibility of cross-contamination: the re-circulated air has been conditioned and returned to the same room. In general, re-circulating air units (fan coils.) are provided with MERV 6 to MERV 8 filters. Using MERV 13 would substantially increase the energy consumption to condition a space without significantly improving the indoor air quality within the space. Imposing such a requirement would also cause most commercial systems to be ineligible for achievement of this credit, and may cause the other beneficial aspects of this credit (walk-off mats and isolation of harmful contaminants) not to be incorporated. Please clarify whether MERV 13 filtration is necessary for air re-circulated within a space.